Made a 1600 ml yeast starter using a 2000 ml flask . Sometime during the night the krausen was pushed up through the neck and pushed out the foam stopper to spill over the edges. Thus, since this strong activity resulted in the starter being exposed to the external air I am wondering if I should keep the yeast from this starter? My concerns are will there be much yeast remaining in the starter since this was a top cropping yeast strain and could airbourne yeast create a problem for this starter.